Tungsten inert gas (TIG) welding became an overnight success in the 1940s for joining
magnesium and aluminium. Using an inert gas shield instead of a slag to protect the weldpool,the process was a highly attractive replacement for gas and manual metal are welding. TIG has played a major role in the acceptance of aluminium for high quality welding and structural applications. The process may employ direct current with positive or negative electrode or alternating current. In general, ac is preferred for welding aluminum and magnesium. Direct current electrode negative is preferred for welding most other materials and for automatic welding of thick aluminum. Thin magnesium sometimes is welded with direct current electrode positive. When ac is used with argon shielding, an arc cleaning action is produced at the joint surfaces on aluminum and magnesium. This cleaning action removes oxides and is particularly beneficial in reducing weld porosity when welding aluminum. When using dc, helium may be used as the shielding gas to produce deeper penetration. However, stringent precleaning of aluminum and magnesium parts is required with helium shielding. Argon and helium mixtures for gas shielding can provide some of the benefits of both gases.
Regardless of polarity, a constant current (essentially vertical volt-ampere characteristic) welding power source is required. In addition, a high-frequency oscillator is generally incorporated in power sources designed for GTAW. High-frequency can be employed with dc to initiate the arc instead of touch starting to minimize tungsten electrode contamination. Normally, the high frequency is turned off automatically after arc ignition. The high frequency power is normally operated continuously with ac to maintain ionization of the arc path as the arc voltage passes through zero.

Tungsten inert gas (TIG) welding became an overnight success in the 1940s for joining
magnesium and aluminium. Using an inert gas shield instead of a slag to protect the weldpool,the process was a highly attractive replacement for gas and manual metal are welding. TIG has played a major role in the acceptance of aluminium for high quality welding and structural applications. The process may employ direct current with positive or negative electrode or alternating current. In general, ac is preferred for welding aluminum and magnesium. Direct current electrode negative is preferred for welding most other materials and for automatic welding of thick aluminum. Thin magnesium sometimes is welded with direct current electrode positive. When ac is used with argon shielding, an arc cleaning action is produced at the joint surfaces on aluminum and magnesium. This cleaning action removes oxides and is particularly beneficial in reducing weld porosity when welding aluminum. When using dc, helium may be used as the shielding gas to produce deeper penetration. However, stringent precleaning of aluminum and magnesium parts is required with helium shielding. Argon and helium mixtures for gas shielding can provide some of the benefits of both gases.
Regardless of polarity, a constant current (essentially vertical volt-ampere characteristic) welding power source is required. In addition, a high-frequency oscillator is generally incorporated in power sources designed for GTAW. High-frequency can be employed with dc to initiate the arc instead of touch starting to minimize tungsten electrode contamination. Normally, the high frequency is turned off automatically after arc ignition. The high frequency power is normally operated continuously with ac to maintain ionization of the arc path as the arc voltage passes through zero.